A wheel bearing apparatus that can support a wheel of vehicle, with respect to a suspension apparatus, and incorporating a rotation speed detecting apparatus to control the anti-lock braking system (ABS) and detecting the rotation speed of the wheel is generally known. Such a bearing apparatus is generally provided with a sealing apparatus arranged between the inner and outer members rotating relative to each other via rolling elements contained between them. The sealing apparatus is integrally formed with a magnetic encoder with magnetic poles alternately arranged along its circumference. A rotation speed detecting apparatus includes the magnetic encoder and a rotation speed sensor to detect change of magnetic poles of the magnetic encoder caused by the rotation of a wheel.
A rotation speed sensor mounted on a knuckle, after the wheel bearing apparatus is mounted on the knuckle forming a suspension apparatus, is generally known. However, recently there has been proposed a wheel bearing apparatus incorporating a rotational speed detecting apparatus. The rotation speed sensor is built into the wheel bearing in order to solve complexity in adjusting operation of the air gap, between the rotation speed sensor and the magnetic encoder, and to reduce the size of the wheel bearing apparatus.
FIG. 8 is one example of a wheel bearing apparatus incorporating a rotational speed detecting apparatus. This wheel bearing apparatus has an outer member 51 to be secured to a knuckle (not shown) forming a stationary member. An inner member 52 is inserted into the outer member 51 via double row balls 53, 53. The inner member 52 includes a wheel hub 55 and an inner ring 56 fit onto the wheel hub 55.
The outer member 51 has an outer circumference with an integrally formed body mounting flange 51b. The outer member inner circumference includes double row outer raceway surfaces 51a, 51a. The inner member 52 is formed with double row inner raceway surfaces 55a, 56a arranged opposite to the outer raceway surfaces 51a, 51a of the outer member 51. One inner raceway surface 55a of the double row inner raceway surfaces 55a, 56a is integrally formed on the outer circumference of the wheel hub 55. The other inner raceway surface 56a is formed on the outer circumference of the inner ring 56. The inner ring 56 is press-fit onto a cylindrical portion 55, axially extending from the inner raceway surface 55a, of the wheel hub 55. Double row balls 53, 53 are contained between the outer and inner raceway surfaces and are freely rollably held by cages 57, 57.
The wheel hub 55 is integrally formed with a wheel mounting flange 54 for mounting a wheel (not shown) on its outer circumference. The inner ring 56 is axially secured by a caulked portion 58. The caulked portion 58 is formed by plastically deforming the end of the cylindrical portion 55b. A seal 59 and a cover 63 are mounted on both ends of the outer member 51 to prevent leakage of lubricating grease sealed within the bearing and entry of rain water or dust from the outside into the bearing.
A magnetic encoder 60 is press-fit onto the outer circumference of the inner ring 56. The magnetic encoder 60 has an annular supporting member 61 formed from magnetic metal sheet. The annular support member 61 has a substantially L-shaped cross-section. An encoder body 62 is adhered to the side of the annular supporting member 61. The encoder body 62 is a permanent magnet formed of rubber mingled with ferrite powder. The magnet has N and S poles alternately arranged along the encoder body 62.
The synthetic resin cover 63 is formed with a bottomed cylindrical configuration. Its cylindrical portion 63a is press-fit into the inner circumference of the inner-side end of the outer member 51. The lid (or bottom) portion 63b closes an opening of the outer member 51. The cylindrical portion 63a is formed with a flange 64 that abuts the end face of the outer member 51. Thus, it is possible to exactly position the whole cover 63 relative to the outer member 51 in the axial direction. Accordingly, it is possible to easily carry out the position control of the sensor 69 mounted on the cover 63.
Also as shown in FIG. 9, the lid portion 63b of the cover 63 is formed with a cylindrical sensor mounting portion 65. An insert portion 69a of a sensor 69 is inserted into a sensor mounting bore 66 formed in the inner circumferential side of the sensor mounting portion 65. A metal core 67, with a bottomed cylindrical configuration, is integrally molded with the cover 63 over a region from the inner circumference of the cylindrical portion 63a to the inner surface of the lid portion 63b. The metal core 67 has a cylindrical portion 67a integrally molded with the cylindrical portion 63a of the cover 63. A lid portion 67b forms a bottom of the cylindrical portion 67a and closes an opening of the sensor mounting bore 66 opposing the encoder body 62.
The metal core 67 is formed from non-magnetic steel sheet with a thickness of about 0.3 mm. The presence of the lid portion 67b increases the strength of the cover 63. The non-magnetic property of the metal core 67 does not provide negative influence to the accuracy of detecting the rotation speed.
The sensor 69 has an outer cover of synthetic resin and is mounted on the cover 63 by inserting the insert portion 69a into the sensor mounting bore 66 of the cover 63. The insert portion 69a opposes the encoder body 62 via a predetermined axial gap with the lid portion 67b of the metal core 67 sandwiched between. The insert portion 69a at a position near the opposing portion of the encoder body 62 includes a detecting portion (not shown) to detect change of the magnetic field generated by rotation of the magnetic encoder 60. This detecting portion can output electric signals of the sensor 69 via an output cable 68.
As described above, the opening portion of the sensor mounting bore 66 of the cover 63 opposing the encoder body 62 is perfectly closed by the lid portion 67b of the metal core 67 by the non-magnetic steel sheet. Thus, no foreign matter can enter into the inside of the wheel bearing apparatus. It has excellent sealability of the whole wheel bearing apparatus as compared with a sensor mounting bore of through-bore type which is not covered by any member (see Japanese Patent No. 4286063).
In such a wheel bearing apparatus incorporating a rotation speed detecting apparatus of the prior art, peeling (or separation) or small gaps tend to be caused by a difference of thermal expansion caused by the change of temperature due to thermal shock in the joined portions between the metal core 67 and the synthetic resin cover 63. The joined portions are between the cylindrical portions 67a of the metal core 67 and the cylindrical portion 63a of the cover 63 as well as between the lid portions 67b of the metal core 67 and the lid portion 63b of the cover 63. Thus, it is difficult to maintain the initial sealability for a long term. In addition, it is also difficult to firmly keep sealability if there is any chatter marks or scratches caused by cutting on the inner circumference of the end of the outer member 51 into which the cover 63 is press-fit.